We know EBS Snapshots allows to create a block-level, point-in-time copy of volumes for backup, or disaster-recovery purposes. Snapshots are incremental, only data modified since the last snapshots are copied again. One can share snapshots between AWS Regions, or AWS Accounts. EBS volume can be created based on a snapshot. The new volume begins as an exact replica of the original volume that was used to create the snapshot.
When one restores volumes from snapshots, they are available for use almost instantaneously. In the background, EBS lazy loads the data from the snapshot as the operating systems accesses the blocks, this reduces the I/O performance of the volume until it is fully initialized. Some I/O demanding workloads however need the volume to operate at full capacity as soon as it is available. This is AWS introduced Fast Snapshot Restore (FSR). Once enabled, FSR allows to create volumes that deliver their maximum performance and do not need to be initialized.
Many AWS customers are sharing their snapshots with other AWS Accounts, and there are many reasons to do this. One might want to centrally prepare and manage golden AMIs. In the context of Disaster Recovery (DR), an organization's policies might require to store all backups in one dedicated account.
Till few days back, only the AWS Account owning the snapshot could enable FSR. But recently AWS has released a new feature with which you can enable Fast Snapshot Restore (FSR) on snapshots shared with you.